Position encoders are used to accurately determine a position difference between elements of a device or system. Conventional position encoders are either incremental position encoders or absolute position encoders, but not both. An incremental position encoder provides position information indicating the change from a prior position, while an absolute position encoder provides absolute position information indicating a specific position regardless of prior position. Position encoders are used in automated manufacturing, gimbaled systems, and elsewhere when accurate positional information is desired. In gimbaled-camera systems, for example, absolute position encoders may be used for accurate line-of-sight reconstruction in guidance.
Some conventional position encoders use separate encoder tracks for each bit of a Grey code, in which only one bit of the code changes at a time. Detectors are used to detect which bit changes to determine a position. One problem with this arrangement is that higher resolution requires a high number of separate encoder tracks. Another problem is that this arrangement is highly sensitive to contamination, which results in erroneous position information.
Thus, there is a general need for an improved position encoder and method for determining position of an encoder track. There is also a need for a position encoder and method where the unambiguous range may be increased almost without limit. There is also a need for a position encoder and method where the unambiguous range may be increased without degrading absolute accuracy. There is also a need for a position encoder and method with an increased unambiguous range without a significant increase in size or complexity. There is also a need for an optical position encoder and method that is less sensitive to contamination. There is also a need for a gimbaled system with improved line-of-sight tracking having at least some of the preceding benefits.